So-called "donut" oil coolers were invented approximately 20 years ago. This type of oil cooler is a heat exchanger having a round shape with a central opening extending therethrough. Perhaps the earliest example in the patent literature is found in commonly assigned U.S. Pat. No. 3,743,011 issued to Donald J. Frost in 1973. With the progression of time, donut oil coolers have seen increasing popularity because of the relatively high efficiency and small size. Another important feature is their ability to be mounted directly on the engine block of an internal combustion engine at the location ordinarily reserved for the oil filter. The oil filter then, in turn, is mounted on the donut oil cooler, on the side thereof opposite from the block. Two hoses are then connected to the donut oil cooler and to the vehicle coolant system.
Within the donut oil cooler, a stack of individual heat exchange units is located. Engine oil passes through the donut oil cooler to the filter and then is returned through the donut oil cooler to the engine, directly through the engine block. On one of the passes through the donut oil cooler, preferably the pass prior to filtering, the oil is passed through the stack of individual heat exchange units. Engine coolant is flowed about the exterior of the stack to achieve heat rejection from the oil to the engine coolant.
Because of the simplicity, compactness and ease of installation, donut oil coolers have achieved a great deal of popularity and the end of their usefulness is not in sight.
The present invention is directed to an improvement in a donut oil cooler, and more particularly, to the elimination of the need for external coolant lines to be connected between the donut oil cooler and engine cooling system.